VPD in flowering

[flylowgethigh]

My VPD is too humid by about 10 points, it's 60% and should be 50% humidity. I am wondering if this affects the quality of the flowers by allowing moisture to enter through the leaves instead of being sucked up by the roots, along with the nutes.

Is that why a lower RH is suggested for flower?

 

[RottyRzr]

Im not gonna try to answer your question but I will say that I grow indoors and have had bud rot issues on larger colas if humidity get above 55%. i bought a dehumidifier and am running it at 50%. Im hoping that helps with the current run.
My last run was Brothers Grimm Durban Thai x C99 and it had giant top colas. Big beautiful colas that I had to run support strings to keep them from falling over. About a week before harvest I spotted the dreaded cotton looking mold in them! Im now running lower humidity. I hope 50% is good enough.
By the way, the Durban Thai x C99 that I saved is awesome smoke!

 

[flylowgethigh]

Mold is a concern. I filter the air that is forced into the tent, and that has helped tremendously with SM and PM. I don't want to run my dehuey because it also heats up the room. I used to run a window banger and the dehuey at the same time. Window banger broke.

 

[phyfusion]

Im not gonna try to answer your question but I will say that I grow indoors and have had bud rot issues on larger colas if humidity get above 55%. i bought a dehumidifier and am running it at 50%. Im hoping that helps with the current run.
My last run was Brothers Grimm Durban Thai x C99 and it had giant top colas. Big beautiful colas that I had to run support strings to keep them from falling over. About a week before harvest I spotted the dreaded cotton looking mold in them! Im now running lower humidity. I hope 50% is good enough.
By the way, the Durban Thai x C99 that I saved is awesome smoke!

I have a backlog of seeds from BG and this is one strain in my inventory- havent grown yet. Do you have any images by chance?

 

[RottyRzr]

I have a backlog of seeds from BG and this is one strain in my inventory- havent grown yet. Do you have any images by chance?

Sorry I don't have any pics. I recently deleted a bunch of photos, those included. iPhone use to have a recently deleted photo file that kept deleted photos for 30 days but I looked today and couldn't find it. I guess one of the updates got rid of it?

 

[Crooked8]

Vpd during veg should be .7-1.0
Vpd weeks 1-3 should be .9-1.1
Vpd weeks 4-6 should be 1.0-1.2
Vpd weeks 7-9 should be 1.2-1.4

 

[Lester Beans]

For best end product RH needs to be 45 or lower in flower.

 

[Crooked8]

For best end product RH needs to be 45 or lower in flower.

Not in early flower, i agree at the end getting it down, but you should not be that low in the first 3 weeks ime.

 

[flylowgethigh]

Humidity is what makes summertime growing more of a pain than winter. I wish my tent was down around 45-50% now, making the plants suck the juices (and goodies) through the stems instead of through the leaf pores.

 

[audiohi]

My VPD is too humid by about 10 points, it's 60% and should be 50% humidity. I am wondering if this affects the quality of the flowers by allowing moisture to enter through the leaves instead of being sucked up by the roots, along with the nutes.

Is that why a lower RH is suggested for flower?

VPD really shows how moisture will evaporate from the leaves. So, if water isn't evaporating away from the stomata, the plant won't pull more from the roots. If your plant stops transpiring, it will affect the quality.

The low humidity is to inhibit mold growth.

Separate but related.

 

[Crooked8]

VPD really shows how moisture will evaporate from the leaves. So, if water isn't evaporating away from the stomata, the plant won't pull more from the roots. If your plant stops transpiring, it will affect the quality.

The low humidity is to inhibit mold growth.

Separate but related.

Exactly, which is why you would NOT want it super low rh during early flower. Youre reducing transpiration capabilities which directly impacts growth rates. Lowering rh and temps towards the end will reduce fungal growth potential and increase quality.

 

[Ca++]

Did I miss how many weeks?
I would be perfectly happy with 60%, until it became a mold risk.

It's not going to stop the plant taking on water. It's within the range a plant can accommodate. Lower water usage that might occur, will just mean raising EC, so they still get enough food.
If you ran lower RH like 45% then the stomata would be closing. That is not good for co2 intake, which is their primary job. They want to be open to get that air, but drying effects close them. 60% is actually nice imo. I have never wanted to get below 50%, and rarely achieve that low tbh. I think what little I loose to mold, I gain though better plants. Plant selection is where mold resistance is mainly achieved.

Data logs suggest my final weeks were 55-62% at the inlet, as it keeps raining. It would be higher within, of course. No losses, but it's not all chopped yet. I might loose some, but what remains will of done better at 60% than 50% (which is not good for cannabis, we know this)

 

[flylowgethigh]

My tent runs about 8-10% higher RH inside than the air being pumped in. I increase the air throughput the latter part of flowering to try to get rid of the moist air. A dehuey in the lung room that I could exhaust the hot air stream outside would be best.

 

[Ca++]

That ones a bit cheap. Most have an umbilical cord you can actually unplug. Not a constant tether, like pictured.
Being an AC, you can bet on finding a unit around 7000btu. Around 40L? but if you really want it working at 45% that will be drastically reduced. I'm not sure this type of dehu is even capable below 30%. So certainly, to get 50%, you need some over size equipment. Though the question of extract rates is hugely important. With 7000btu, you may not even need extract for temperature reasons. So this might pull the water from a 1.4 x 1.4 tent

 

[flylowgethigh]

What is that?

 

[Ca++]

Windows Bangers are just not seen in the UK. We need AC barely ever, so won't loose a window for one.
If we did have them, the practice of using them where needed, would likely spill out into places like Scotland, where they would be more use as heat pumps. This would kill our diverse market of portable solutions, that can go away for the winter.
It's a portable mini split. Most come with a quick release umbilical, so you can feed them through small holes.

You do get them, just as we can get bangers. It's just not the norm. Here, a banger might go in the bosses office, if it's the only office getting AC, in some industrial setting. Or where a storage room needs keeping cool, but nowhere else. In the US, the aircon business actively keeps the reputation of portable kit, in the gutter. They know they can sell you a proper install, so you are not to know if you don't need one

 

[Crooked8]

Windows Bangers are just not seen in the UK. We need AC barely ever, so won't loose a window for one.
If we did have them, the practice of using them where needed, would likely spill out into places like Scotland, where they would be more use as heat pumps. This would kill our diverse market of portable solutions, that can go away for the winter.
It's a portable mini split. Most come with a quick release umbilical, so you can feed them through small holes.

You do get them, just as we can get bangers. It's just not the norm. Here, a banger might go in the bosses office, if it's the only office getting AC, in some industrial setting. Or where a storage room needs keeping cool, but nowhere else. In the US, the aircon business actively keeps the reputation of portable kit, in the gutter. They know they can sell you a proper install, so you are not to know if you don't need one

Ahh i dunno man they have marketed mini split setups to growers too afraid to hire an hvac tech here for a decade or more. However, they typically suck and never rock out like a true condenser with a blower. Endless mechanical issues, leaks, icing over etc.

 

[Crooked8]

Windows Bangers are just not seen in the UK. We need AC barely ever, so won't loose a window for one.
If we did have them, the practice of using them where needed, would likely spill out into places like Scotland, where they would be more use as heat pumps. This would kill our diverse market of portable solutions, that can go away for the winter.
It's a portable mini split. Most come with a quick release umbilical, so you can feed them through small holes.

You do get them, just as we can get bangers. It's just not the norm. Here, a banger might go in the bosses office, if it's the only office getting AC, in some industrial setting. Or where a storage room needs keeping cool, but nowhere else. In the US, the aircon business actively keeps the reputation of portable kit, in the gutter. They know they can sell you a proper install, so you are not to know if you don't need one

double post

 

[thugpoet]

Im not gonna try to answer your question but I will say that I grow indoors and have had bud rot issues on larger colas if humidity get above 55%. i bought a dehumidifier and am running it at 50%. Im hoping that helps with the current run.
My last run was Brothers Grimm Durban Thai x C99 and it had giant top colas. Big beautiful colas that I had to run support strings to keep them from falling over. About a week before harvest I spotted the dreaded cotton looking mold in them! Im now running lower humidity. I hope 50% is good enough.
By the way, the Durban Thai x C99 that I saved is awesome smoke!

Wow, that is really unlucky a NLD molding at 55%. I've run Afghanicas with consistent 65-70% RH and no fungi problem indoors (as long as you have adequate ventilation and defoliate). I guess big dense buds are a liability no matter the genotype.

Too much humidity is not ideal because it supposedly degrades the terpenes, but too high of a VPD produces pretty bad-tasting weed as well. Going below 50% RH could put you at risk of having permanently squatting spider mites.
I think anything between 50-60% is fine though and pretty close to optimal (obviously depending on temps).

Some people swear by doing low temp low RH to get good VPD values and maximize the Terpenes.

Cannamicably,

Thug

 

[Ca++]

Ahh i dunno man they have marketed mini split setups to growers too afraid to hire an hvac tech here for a decade or more. However, they typically suck and never rock out like a true condenser with a blower. Endless mechanical issues, leaks, icing over etc.

Hey bud.

My newest unit is 14 years, and I dread to think how old my oldest is. It's loosing some efficiency now, but uses a proper blower fan and buckets out 13c air, when it's about 25c going in. I have to plumb in the drain, as it's trickling more than dripping at times. It uses just the same parts as a fixed install, so there should be no difference in reliability. Just like your domestic fridge or freezer, they should really last till they rust away.

The cold bit shouldn't be getting below freezing, with enough air over it. Though the wider fin spacing of a freezer will always be more resistant to freezing than the closer spacing of a chiller. These are things the manufacturer should be taking care of though.

My fridge man won't even look at a portable unit. He wants to tell me they are different, but fails at a weak jaw movement. He knows I changed out all the mechanical controls on our walk-ins, to programmable stuff with digital displays. Controllers I jog along for him when he doesn't want to wait for the cycle time. So when I tell him it's the same, he just chews air. Our main aging problem there, is the acidic nature of food stuffs, eating the evaporator over time. He want hear of leak seal. Again, he's chewing air, with no words coming out. He was hard to find though, so we let the old gizzard get on with it.

I have to wonder.. is the resin in the air going to eat away at the alloy or copper cores. All them voc's that we actively try to get more of. My units don't get used in sealed rooms, where that risk exists. Like the OP, I treat the air going in.

You know.. that might be it. Years ago we knew of a guy changing quite a few dehu's on a yearly basis. They were always caked up, and a disposal problem. I had clean forgot about this, as it was an isolated case for me. Strongest tested weed ever found in the UK, when they got it. I just heard the story, as I was asked why it might be happening. I was clueless.. It must be 30 years ago.